How to get the source status and target status of the transition in Jira Validator's validate() method?

I’m trying to use one validator (package for multiple Jira transition, such as from “Ready” to “In Progress”, “In Verification” to “Done”… So in when the every transition is called, I can catch the event in a same validate() method. In the validate() method of the validator, I want to determine the source (and target) status of the current transtion. I’ve checked the input Map transientVars, Map args, and PropertySet ps, but could not find any useful information about the “source” and “target” status of the current transition. Is there some way to do that? Or I have to use different validators for different transition?

public class ReleaseIssueValidator implements Validator {
    public void validate(Map transientVars, Map args, PropertySet ps) throws WorkflowException {
        //get statuses here?